The Kane proposal1,2 for a silicon-based quantum computer uses the nuclear spin of phosphorus nuclei (I=½) as the qubits embedded in isotopically pure 28Si(I=0). At low temperatures the donor electron remains bound to the P nucleus and surface “A” gates control the hyperfine interaction between nuclear and electron spins, enabling polarization of the two. The two P donors need to be ˜20 nm apart to allow the adjacent donor electron wavefunctions to overlap. Coupling between adjacent donor electrons is achieved using separate surface “J” gates, enabling an electron mediated interaction between qubits. FIG. 1(a) shows this proposed structure.
A number of patent applications and papers are relevant to the building of such a device, and these are cited below:    1Kane, B. E. A silicon-based nuclear spin quantum computer. Nature 393, 133 (1998).    2Kane, B. E. Patent Application PCT/AU98/00778.    3Vrijen, R., Yablonovitch, L., Kang Wang, Hong Wen Jiang, Balandin, A, Roychowdhury, V., Mor, T., DiVincenzo, D. Electron-spin-resonance transistors for quantum computing in silicon-germanium heterostructures. Phys. Rev. A 62, 012306/1–10 (2000).    4Swartzentruber, B. S., Mo, Y. W., Webb, M. B. & Lagally, M. G. Scanning tunneling microscopy studies of structural disorder and steps on Si surfaces. J. Vac. Sci. Tech. A 7, 2901 (1989).    5Hata, K., Kimura, T., Ozawa, S. and Miyamoto, N. How to fabricate a defect free surface. J. Vac. Sci. Technol. A 18, 1933 (2000).    6Hata, K., Yasuda, S. and Shigekawa, H. Reinterpretation of the scanning tunneling microscopy images of the Si(100)2×1 dimers. Phys. Rev. B. 60, 8164 (1999).    7Oura, K., Lifshits, V. G., Saranin, A. A., Zotov, A. V. & Katayama, M. Hydrogen interaction with clean and modified silicon surfaces; Surf. Sci. Rep. 35, 1 (1999).    8Hamers, R. J., Avouris, Ph. & Bozso, F. Imaging of chemical-bond formation with the scanning tunneling microscope. NH3 dissociation on Si(001) Phys. Rev. Left. 59, 2071 (1987).    9Thirstrup, C., private communication    10Wang, Y., Bronikowski, M. J. & Hamers, R. J. An atomically-resolved STM study of the interaction of phosphine (PH3) with the silicon (001) surface. J. Phys. Chem. 98, 5966 (1994).    11Hill, E., Freelon, B., Ganz, E. Diffusion of hydrogen on the Si(001) surface investigated by STM atom tracking. Phys. Rev. B 60, 15896 (1999).    12Lin, D. S., Ku, T. S., and Chen, R. P. Interaction of phosphine with Si(100) from core-level photoemission and real-time scanning tunneling microscopy Phys. Rev. B 61, 2799 (2000).    12Lin, D. S., Ku, T. S., and Chen, R. P. Interaction of phosphine with Si(100) from core-level photoemission and real-time scanning tunneling microscopy Phys. Rev. B 61, 2799 (2000).    14Wang, Y., Chen, X. and Hamers, R. J., Atomic-resolution study of overlayer formation and interfacial mixing in the interaction of phosphorus with Si(001) Phys. Rev. B 50, 4534 (1994).    15Zhi-Heng Loh, Kang, H. C. Chemisorption of NH3 on Si(100)2×1: A study by first-principles ab initio and density functional theory. J. Chem. Phys. 112, 2444–2451 (2000).    16Northrup, J. E. Theoretical studies of arsine adsorption on Si(100). Phys. Rev. B 51, 2218–2222 (1995).
To date there have been no STM studies of the incorporation of single phosphorus atoms from a dopant source such as phosphine into silicon.
This invention demonstrates, for the first time, achievement of a number of the intermediate products and steps necessary to produce a silicon based atomic-scale device such as a quantum computer in line with the Kane proposal.